1. Field of the Invention
The present invention relates to a hydraulic mount for a vehicle that reduces the number of assembly processes and improves productivity of the hydraulic mount. In addition, the hydraulic mount of the present invention eliminates the formation for a joint formed due to a reinforcement plate of a membrane reduces cost and weight of the hydraulic mount for the vehicle.
2. Description of the Related Art
In general, a power train including an engine and a transmission of a vehicle is mounted on an engine compartment using an engine mount and a transmission mount, and a roll rod to be supported at a sub frame. In this case, the sub frame is combined with a vehicle frame to form the engine compartment.
A method of mounting the engine and the transmission may be classified into an inertia support method and a central support method. The inertia support method uses a principal axis of inertia of the engine and is classified into a four-point support method and a three-point support method according to the number of mounts. In the three-point support method, the engine mount coupled to the engine and the transmission mount coupled to the transmission are mounted on the vehicle, and the roll rod is mounted on the sub frame. Furthermore, an inertia three-point support method is mainly used in front-wheel drive vehicles. Since the weight and cost of a sub frame increases for the inertia four-point support, the power train is supported by the three-point support method using an ‘H’-shaped sub frame.
Moreover, to effectively reduce vibration and noise in the vehicle, the characteristics of mounts may be adjusted for reduction to be substantially high at vibration low speed and a dynamic spring constant to be substantially low at vibration high speed. To satisfy these characteristics, a hydraulic mount for a vehicle may be applied to a bottom surface of an insulator formed of rubber. The engine mount is usually manufactured as a hydraulic mount.
The hydraulic mount has a structure in which wide area vibration, such as vibration with low frequency/high amplitude or vibration with high frequency/low amplitude that is input when the engine is driven, may be reduced using viscosity of a fluid and characteristics of rubber. A structure of an engine mount 1 for a vehicle according to the related art will now be described with reference to FIG. 1.
As illustrated in FIG. 1, the vehicle engine mount 1 having the shape of a hydraulic mount according to the related art includes a center bolt 10 coupled to an engine, an inner core 20 through which the center bolt 10 passes, an insulator 30 formed of rubber and integrated with the inner core 20 by a vulcanization molding process, an outer pipe 40 in which a lower portion of the insulator 30 is inserted, which is disposed to surround the insulator 30 and is coupled to a vehicle via a mounting bracket (not shown), a diaphragm 50 disposed on the bottom surface of the insulator 30, an orifice lower plate 60 disposed on a top surface of the diaphragm 50 from a lower interior of the insulator 30, and a membrane 80 inserted between an interior of the orifice lower plate 60 and an orifice upper plate 70.
Furthermore, an upper chamber 2 is a space is formed between the insulator 30, the orifice lower plate 60, and the membrane 80 in which a fluid is sealed, and a lower chamber 3 is a space formed by the membrane 80, the orifice lower plate 60, and the diaphragm 50, is partitioned off from the upper chamber 2 by the membrane 80 and is disposed below the upper chamber 2.
Additionally, an inertia track 61 is disposed on a circumference of the orifice lower plate 60 in a serpentine shape along circumferences of the upper chamber 2 and the lower chamber 3. A top surface of the serpentine inertia track 61 is covered by the orifice upper plate 70. An inner path of the inertia track 61 is connected to the upper chamber 2 via an opening 71 formed through the orifice upper plate 70. Thus, when an inner volume of the upper chamber 2 is reduced, the fluid in the upper chamber 2 is moved to the inertia track 61 via the opening 71 of the orifice upper plate 70.
In the hydraulic engine mount 1 for the vehicle having the above structure, when vibration is transmitted from the engine, the inner core 20 and the insulator 30 are deformed such that the volume of the upper chamber 2 is adjusted. In particular, the fluid corresponding to the adjusted volume is moved from the upper chamber 2 to the lower chamber 3. Specifically, the fluid flows into the serpentine inertia track 61 via the opening 71 of the orifice upper plate 70 and then flows along the inertia track 61 (see arrow A), or when the fluid passes through a gap between the membranes 80 (see arrow B), shock load is reduced, as illustrated in FIG. 2.
In other words, shock from the top surface of the engine mount 1 is transmitted to the fluid in the upper chamber 2. The shock is converted into thermal energy when the fluid passes through the gap between the membranes 80, and is reduced. The remaining shock load is transmitted to the fluid in the lower chamber 3, and a shock quantity is again reduced.
When the quantity of the fluid that corresponds to the deformed volume of the inner core 20 and the insulator 30 is larger than the movement quantity of the fluid that passes through the gap between the membranes 80, in other words, when vibration with low frequency and high displacement occurs, the fluid does not pass through the gap between the membranes 80 and flows along the serpentine inertia track 61. In this case, vibration with a particular frequency is resonant with the fluid in the serpentine inertia track 61, and thus a large attenuation force is generated.
On the other hand, when vibration with high frequency and low displacement is input from the engine, displacement is within the range of movement of the membrane 80. Thus, the quantity of the fluid that corresponds to the deformed volume of the inner core 20 and the insulator 30 does not pass through the serpentine inertia track 61 having a relatively large flow resistance but passes the gap between the membranes 80 having a relatively small flow resistance. In this case, the fluid passes through the lower chamber 3 from the upper chamber 2 within a substantially short amount of time, and thus vibration is reduced.
The purpose of the hydraulic engine mount 1 is to attenuate a particular frequency and to reduce dynamic characteristics that may not be achieved using an existing rubber type engine mount. The hydraulic engine mount 1 improves ride performance by giving attenuation characteristics in a frequency band of 10 to 12 Hz.
However, a hydraulic engine mount for a vehicle having a dual orifice structure, as illustrated in FIG. 3, has been developed to increase a dielectric constant in a frequency band of 100 to 130 Hz.
In the dual orifice structure, a secondary nozzle 72 having a predetermined height (i.e., 5 mm or higher) connects an installation space between the upper chamber 2 and the lower membrane 80, and protrudes from a center of the orifice upper plate 70 upwards. Furthermore, vibration (e.g., 12 Hz) is attenuated by primary orifice action in which the fluid is moved along the inertia track 61, and dynamic characteristics (130 Hz) are reduced by secondary orifice action in which the fluid flows via the secondary nozzle 72, wherein the secondary orifice action is separate from an orifice action in which the fluid passes through the gap between the membranes 80.
In the primary orifice action, vibration of a power train is suppressed by damping in a frequency band of 10 to 12 Hz to improve vehicle travel performance, and in the secondary orifice action, dynamic characteristics in a frequency band of 130 Hz are reduced to improve NVH (noise vibration) performance by increasing the dielectric constant. In this way, in the dual orifice structure, ride performance and NVH performance may be simultaneously improved (e.g., reduction of vibration in other frequency regions).
However, in the hydraulic mount having the dual orifice structure according to the related art, a joint may be formed due to the structure of a free movement type membrane, and the number of assembly processes may increase. Specifically, as illustrated in FIGS. 4 through 6, a configuration for the dual orifice structure includes three components, such as the orifice upper plate 70, the orifice lower plate 60, and the membrane 80. Furthermore, a reinforcement plate 81 formed of steel is inserted in the membrane 80. Thus, when the membrane 80 moves freely, the reinforcement plate 81 is excited between the orifice upper plate 70 and the orifice lower plate 60 due to high frequency vibration thereby causing a joint to be formed (see FIG. 4).
In addition, since the membrane 80 is inserted between the orifice upper plate 70 and the orifice lower plate 60, four rivets 60a are required for assembly to fix the orifice upper plate 70 and the orifice lower plate 60 in addition to outer pipe curling fixing. Thus, addition components are required thereby increasing the assembly process of the hydraulic mount.
Furthermore, due to the protrusion structure and height of the secondary nozzle 72 formed on the orifice upper plate 70, when tuning including installation of a plunger in the upper chamber 2 is performed, a space in which the plunger is to be installed, may be insufficient, tuning may be limited, and the size of the hydraulic mount for the vehicle may increase.